Chevy & GMC Vans

While chasing down a low fuel pressure issue this past weekend I found that the breather hose that connects to the tbi has been belching excessive amounts of oil right on to my pressure regulator. My pcv valve is working fine and the vaccuum on the pcv line will just about suck your thumb print off.
I'm beginning to wonder if something is missing off the breather side of the pcv system. There is no screen or oil catch can of any kind, just a plastic elbow into the rocker arm cover and the hose. I understand as rpm goes up, the intake vacuum increases and the pcv vacuum decreases, but this seems like a real design flaw. Any input is appreciated.

Sounds like everything is getting old and gunky. One thing you might want to do is remove your TBI and rebuild it. Rebuilding is just cleaning it and putting new gaskets and seals in. The bottom of the TBI gets REALLY gunked up in the PCV area.

10-4 on the tbi gunk. I rebuilt it about 3 years ago. Scraped all kinds of crud out of the bottom of the throttle body. Could be time again.
The pcv valve plugs into the rocker cover, but from there down to the crankcase, I have no idea what route the blow-by gas takes. Do the oil return ports in the head also serve to withdraw blow-by gas? Whatever the path, I'm thinking that things are sludged up and not working properly.
I've been hunting on the internet for a labeled diagram of the 4.3 heads to try to understand how the oil return and pcv system work. So far, I haven't found anything.

bump one for me...
anybody know what passages in the heads the pcv system pulls gases through?

lockdoc wrote:Sounds like everything is getting old and gunky. One thing you might want to do is remove your TBI and rebuild it. Rebuilding is just cleaning it and putting new gaskets and seals in. The bottom of the TBI gets REALLY gunked up in the PCV area.

x2. I had another safari a while ago that the TBI was so gunked up that the blowby was shotting oil out of the dipstick. Turned out that the passage inside the TBI when the hose attached to was completely clogged.

got that one covered. The hose to the pcv valve pulls great vacuum. pcv valve is fine.
thanks for the input though. You are definitely right about the pcv port getting plugged up.
What I'm trying to find out is which ports in the cylinder head the blow by gasses pass through to the rocker cover where the pcv valve is located. I'm thinking these may be gunked up.

kings-x59 wrote:got that one covered. The hose to the pcv valve pulls great vacuum. pcv valve is fine.
thanks for the input though. You are definitely right about the pcv port getting plugged up.
What I'm trying to find out is which ports in the cylinder head the blow by gasses pass through to the rocker cover where the pcv valve is located. I'm thinking these may be gunked up.

There are a lot of them, including the passages where the pushrods go. I highly doubt that they are clogged.

Yep, I don't think they would be clogged either (oil return holes). Have you ever seen a SBC head/valley? I think your 4.3 has the same type of setup. Every push rod has a hole and you have a large front and rear oil return holes in the valley.







If not the TBI would look at piston ring blow by.
Are the piston rings old? How many miles on the motor? Have you checked the compression? Does the truck run as well as it used to?

Nope, never seen a head valley.
Thanks for the pics Jinmajay, that helps a bunch. After seeing the size of the oil return passages, you guys must be right. I don't have a point of reference on how it ran new, I got it with 83K miles on it. It has 117K on it now and runs a heck of alot better now than when I got it. I'm sure the rings exhibit the expected wear for the mileage. I haven't checked the compression, but it scoots along just fine.
I think an oil catch can on the crankcase breather hose is in order. I've been doing some reading, oil splatter in the throttle body appears to be a common issue.

post script on my pcv valve. I thought it was ok, but now I think not. I picked one up this morning. even though the weight in the valve was free and would rattle when shaken, the difference in weight between the old valve and the new valve you could discern by holding them in your hand. In spite of repeated sprayings with carb cleaner, the pcv valve apparantly was gunked up.
I also rigged an oil catch on the breather hose between the driver's side rocker cover and the throttle body. I'll post pics and results in a separate post after I've driven it for a week or so.

great!

yep, thanks again Jimnajay for the pics, that broke me lose from my frame of thinking. My baby's running good.
I'm curious now to see how the oil catch works on the breather side of the pcv system. new pcv valve in. most of this mornings commute was really slow. Highways speeds longer than an hour are what I'm after. Oil gets heat soaked, pcv valve is mostly closed at high rpm. i got my first high speed ride home tonight after leaving work at 7pm, grabbed the flashlight and checked to oil catch...nothing in there. So we'll see. One of two things I think. either the oil catch is going to work, or it may be much simpler than that. I might just be using a longer piece of vacuum tubing oriented upwards so the vacuum at high rpm from the upper part of the intake cannot suck oil out of the rocker cover.

man...I think about this s**t to much.....
Astrocrak addiction

kings-x59 wrote:yep, thanks again Jimnajay for the pics, that broke me lose from my frame of thinking. My baby's running good.
I'm curious now to see how the oil catch works on the breather side of the pcv system. new pcv valve in. most of this mornings commute was really slow. Highways speeds longer than an hour are what I'm after. Oil gets heat soaked, pcv valve is mostly closed at high rpm. i got my first high speed ride home tonight after leaving work at 7pm, grabbed the flashlight and checked to oil catch...nothing in there. So we'll see. One of two things I think. either the oil catch is going to work, or it may be much simpler than that. I might just be using a longer piece of vacuum tubing oriented upwards so the vacuum at high rpm from the upper part of the intake cannot suck oil out of the rocker cover.

man...I think about this s**t to much.....
Astrocrak addiction

I agree, you are overthinking this. But glad to hear so far so good.